Noise reduction device having walls therein

ABSTRACT

Disclosed is a noise reduction device, including a pipe-shaped body having an inlet and an outlet, and walls provided in the body to filter noise propagating from the inlet to the outlet, whereby the noise intensity exiting the outlet is less than the noise intensity entering the inlet, the quantity of walls and angle provided between the walls and body being variable to change the performance of noise reduction.

PRIORITY

This application claims priority to an application entitled “NOISEREDUCTION DEVICE HAVING WALLS THEREIN” filed with the KoreanIntellectual Property Office on Oct. 4, 2003 and assigned Serial No.2003-0069765, the contents of which are hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to a noise reduction device, and moreparticularly to a noise reduction device which has an inlet and anoutlet and is formed in the shape of a pipe, wherein walls are providedin the body thereof, thereby filtering some of the noise passing throughthe device, so that the noise in the outlet can be significantlyreduced.

BACKGROUND OF THE INVENTION

Noise problems occur commonly in automobiles as well as machines used inplants. The demand for a noise reduction device, which has a structurethat does not inhibit gas flow in a short-length device is presentespecially in noise generating mechanisms using internal combustionengines, such as motors, power generators, automobiles, etc. Thus, thefollowing description will be provided, focusing on the internalcombustion engine.

The internal combustion engine generates the strongest noise when thefuel is burned inside cylinders of the engines. Thus, mufflers areusually used in order to reduce the strong noise to a suitable level.The noise generated from burning fuel inside an engine is so strong andit is difficult to design a muffler in a to sufficiently reduce it to adesired level due to the limited size of the muffler.

If the muffler can be designed without any limitation on its size, theproblem mentioned above should not occur. But mufflers are designed withconsiderable space limitations resulting in less than optimalperformance.

FIG. 5 shows the muffler (10) of the passenger car model “AVANTE” madeby Hyundai Motor Company, wherein the exhausting gas is arranged to beexhausted after taking a turn in the muffler (10). As a result, sincethe exhausting gas is arranged to flow in the reverse direction twotimes, the exhaust resistance is considerably increased, inhibiting theexhaust gas from completely discharging to the outside.

All mufflers, which are used as noise reduction devices for mostinternal combustion engines, have the same or similar shape as themuffler shown in FIG. 5. The reason that the muffler should be designedas shown in FIG. 5 is because of its compact size due to spacelimitations.

Therefore, in most noise generating mechanisms using internal combustionengines, exhaust gas remains in the engine due to exhaust resistanceresulting in incomplete combustion and loss of power. A tuned mufflerreduces noise and reduces lost power due to exhaust resistance.

Accordingly, noise generating mechanisms using internal combustionengines have a demand to reduce the noise to a suitable level within asmall area, however, conventional technology for noise reduction doesnot satisfy the co-existing demands for noise reduction and a morecomplete flow of the exhaust gas out of the noise reduction device.

Conventional technology has used the muffler shown in FIG. 5 in order toeffectively reduce the noise within a small area, however, in the caseof using the conventional muffler as applied to an internal combustionengine, the power output is reduced and many pollutants are exhausted.

In addition, the conventional muffler has a structure incapable ofdischarging the condensed water completely leading to corrosion.

Further, in the case where noise generating mechanisms such as motorsemit a lot of heat, it is difficult to exhaust the heat from theconventional muffler.

Accordingly, the object of the present invention is to provide animproved noise reduction device, which can reduce noise to a suitablelevel and more fully discharge the exhaust has to the atmosphere.

SUMMARY OF THE INVENTION

In order to achieve the above objects, the present invention provides anoise reduction device, which has an inlet and an outlet and is formedin the shape of a pipe, wherein walls are provided in the body thereof,thereby filtering some of the noise passing through the device, so thatthe noise at the outlet is significantly reduced.

In addition, in order to apply the present invention to automobiles, thenoise reduction device is arranged with straight and angled sections.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention, wherein:

FIG. 1 a shows a cross sectional view of a noise reduction deviceaccording to the present invention, and a vertical sectional view of thedevice, wherein both sides of the device are provided with walls;

FIG. 1 b is a plan view of a muffler designed in accordance with thelower structure of the automobile according to the present invention;

FIG. 2 a is a cross-sectional view of the present invention showing thenoise being filtered by walls;

FIG. 2 b shows a cross-sectional view of an angled section of thepresent invention showing noise dissipating as it hits the wall;

FIGS. 3 a to 3 d are line illustrations of different aspects of thepresent invention explained later in further detail;

FIG. 4 a is a photograph showing the walls provided in the noisereduction device;

FIG. 4 b is a photograph showing the sectional view of the wallsprovided in the device, wherein one end thereof is open so that exhaustresistance is not generated;

FIG. 4 c is an illustration of the walls on two sides of the deviceshowing the ease with which condensed water is discharged;

FIG. 4 d is an embodiment of the present invention as applied toreducing bathroom noise;

FIG. 4 e is an embodiment of the present invention as applied toreducing the noise from a helicopter's engine;

FIG. 5 is a diagram of a muffler from an “AVANTE” made by Hyundai MotorCompany; and

FIG. 6 is an illustration of the present invention showing the sectionalarea of an outlet is designed to be smaller than that of an inlet toprevent secondary noise.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiment of thepresent invention in conjunction with the accompanying drawings.

In FIG. 5, the conventional noise reduction device 10 used in theinternal combustion engine is shaped so that the exhaust resistance isvery high as described above. However, according to the presentinvention, the exhaust resistance is reduced significantly.

First, according to the present invention, as shown in FIGS. 1 a, and 4b, the exhaust resistance of the exhaust gas is reduced to nothing. Thatis, passing the exhausting gas through the present invention is equal toa case wherein the exhausting gas passes through a a typical exhaustpipe of the prior art having an inner diameter as great as the emptyspace formed in the center of the present invention.

Someone might say that the resistance can be increased by the wallsprovided in the present invention, however, actually the space betweenthe walls are packed with air, thus the exhaust gas does not enter thespace because the space is considered full. That is, passing the exhaustgas through the present invention having walls is the same as theexhaust gas passing through a typical exhaust pipe. For easyunderstanding, it is synonymous to pouring sand into the empty spaceformed in the center of the present invention after filling the spacebetween the walls 1 with sand.

Therefore, loss of power due to exhaust resistance of the exhaust gas isnot generated in the present invention.

FIG. 2 a shows an embodiment wherein the present invention is providedwith a plurality of walls 1 inside the pipe 30 so that the noise iscontinuously blocked by the walls (1).

The exhaust gas and the noise are arranged to be exhausted from the leftside to the right side. It can be anticipated that the noise in anoutlet 12 will decrease due to absorption of the walls 1. The wall'sarrangement, position, quantity and other characteristics can be varieddepending on how much noise reduction is desired.

If the effect of noise reduction is too low, the muffler cannot be usedas a noise reduction device, thus an appropriate method for installingthe walls 1 in the present invention should be arranged in order tomaximize the effect of noise reduction. The walls 1 are installed on theinner sides of the pipe. FIG. 4 c shows a plurality of walls 1 providedon both inner sides of the pipe.

FIG. 2 a is an illustration of noise propagating through a section ofthe pipe 30, wherein a plurality of walls 1 are provided perpendicularlyin the present invention which show the sound transfer. However, FIGS. 3a to 3 c, illustrate a second embodiment where the walls 1 are tilted at45°. The principle for blocking the noise is the same, however, theangle reflecting the filtered noise to the center of the presentinvention is slightly different. FIG. 3 c shows a graph optimizing thewall 1 angle in order to maximize the effect of noise reduction.

That is, as shown in FIG. 3 c, when drawing a vertical line from anupper point of a wall 1 (hereinafter referred to as the “head 3”) to thebody 13 of the present invention, the vertical line should meet a bottompoint of an adjacent wall 1 (hereinafter referred to as the “root 2”).Assuming that the installing angle of the wall 1 is θ, the length of thewall is L, and the length between the “roots 2” is l, as in Equation(1).L cos θ=l  {circle over (1)}

When Equation (1) is satisfied, the arrangement of the walls 1 isoptimized. That is, when the value of L cos θ is equal to the value ofl, it is the most preferable to prevent the filtered and reflected noisefrom directly proceeding to the outlet 12.

In this case, it is apparent from FIG. 3 d that the noise filtered bythe walls 1 and bumped against the body 13 of the present inventioncannot directly proceed to the outlet 12. If a wall 1 is installed in amanner that a vertical line from the “head 3” of a wall 1 meets themiddle portion of an adjacent wall 1, then as set forth in Equation (2):l<L cos θ  {circle over (2)}

When the above condition is made, the noise bumped against the body 13of the present invention and reflected from the body 13 cannot alsodirectly proceed to the outlet 12, however, the intervals of the walls 1are unnecessarily close. That is, in this case, the weight of thepresent invention increases without increasing the effect of noisereduction, thus that is not a preferable relation between the walls (1).l>L cos θ  {circle over (3)}

In addition, when the above Equation (3) is satisfied, that is, thedistance between a wall and an adjacent wall is far away from eachother, some of the noise bumped against the body 13 of the presentinvention directly proceeds toward the outlet 12, thereby decreasing theeffect of noise reduction.

As disclosed in the above, in order to maximize the effect of noisereduction by using the walls 1, the walls 1 should satisfy the Equation{circle over (1)}.

Accordingly, if the length of a wall 1 is lengthened, the number ofwalls 1 will decrease, and if the length of a wall 1 is shortened, thenumber of walls 1 will increase. FIG. 3 b shows the relation between thelength and the number of walls 1. In order to make the sectional area ofthe present invention smaller while maintaining an equal the sectionalarea of the exhaust exit, the length (L) of the wall 1 is shortened.

In order to use the present invention as a muffler for an automobile,the length of the wall 1 can be made as short as several millimeters. Inthis case, since the diameter of the present invention is only severalmillimeters bigger than that of a typical exhaust pipe, the presentinvention can be installed in accordance with the lower structure of theautomobile as shown in FIG. 1 b.

The noise passing through the present invention can be classified intotwo types, one is that which enters the space between the walls 1 afterbeing filtered by the walls 1, and the other is that which goes straightthrough the center empty space of the present invention.

Since it is easy to illustrate an example for easy explanation andunderstanding, FIG. 2 a is shown as the example wherein the walls 1 areinstalled perpendicularly against the body 13 of the present invention.

The two walls 1 opposed in the present invention are referred to as aset of walls 1. The noise passing through a set of walls 1 resounds inthe present invention and then is filtered by an adjacent set of walls 1b.

While the noise appears to be reduced at the regular ratio as the noisepasses through each set of walls 1, the ratio actually decreases. Thereason is that sound waves strengthen during straight transmissionrather than the property of spherical wave as the sound waves get awayfrom the source of sound. The phenomenon is shown in FIG. 3 d.

If the present invention is formed with a straight-line type and theactual strength of sound energy after reducing the sound pressure byusing n sets of walls is defined as P_(n), and the strength of soundenergy after reducing the sound pressure by using each set of walls 1 isdefined as α_(k), then as set forth in Equation (4):P _(n)=α₁ . . . α_(k) . . . α_(n)  {circle over (4)}

That is, as in the above Equation (4), the value of the sound pressurein the outlet 12 will be the value multiplied by the strength of thesound energy after being filtered by each set of walls 1. Let us referto FIG. 3 d, which shows the degree of noise being filtered by the walls1. The noise is arranged to enter the present invention having the walls1 from a typical exhaust pipe. A typical exhaust pipe does not interruptthe flow of the noise and allows the noise to be reflected after beingbumped against its inner side, thus the noise enters the presentinvention, making spherical waves continuously. However, after reachingthe present invention, the noise is filtered and reflected by the walls1 of the present invention, thus the property of spherical wave isweakened and the property of straight transmission is strengthened. As aresult, the ratio being filtered by the walls 1 is decreased as shown inFIG. 3 d.

The noise can be largely reduced by the first set of walls 1 because theproperty of spherical wave is maintained strongly as if the source ofsound were at the very front of the first set of walls 1. The ratio ofthe noise filtered by the first set of walls 1 can be differentdepending on the diameter D of the space passing the exhaust gas, theinterval l between roots 2 of the walls 1 and the length of the wall 1 Las shown in FIGS. 3 a, 3 c, and 3 d.

Assuming that the value of α₁ is 0.8, which can be obtained by adjustingthe values of D and l.

If the value of α_(k) is equal to the value of α₁, $\begin{matrix}{{P_{n} = {0.8\quad\ldots\quad 0.8\quad\ldots\quad 0.8}}\quad} \\{= 0.8^{n}}\end{matrix}$

The above formula for noise reduction can only be made in the case ofFIG. 2 a. That is, according to the formula, the degree of noisereduction will be higher as the number of walls 1 is increased.

However, as shown in FIG. 3 d, since the degree of noise reduction isactually decreased, the noise strength in the outlet 12 will be asfollows:P _(n)=0.8·0.89·0.92

Equation {circle over (4)} is the most suitable as the mathematicalexpression for the noise strength passing through the present inventionwithout being filtered by the sets of walls 1, however, actually thevalue may be varied depending on the values of D and l. Also, since thecondition α_(k)<α_((k+1)) appears to be apparent from FIG. 3 d, theratio filtering the noise by using the sets of walls 1 decreases.Accordingly, if designing the present invention as a straight-line typethe effect of noise is reduced.

That is, while noise, which is reflected by an inner surface of atypical exhaust pipe proceeds towards an outlet, it displays theproperty of spherical wave continuously. However, as the noise passesthough the muffler according to the present invention is filtered by thewalls 1 and bumped against the body 13 of the present invention and isthus deflected away from the outlet 12, the property of spherical waveis weakened and the property of straight transmission is strengthened,so that the ratio being filtered by the walls 1 is decreased. Thus, ifdesigning the present invention as a straight-line type, the degree ofnoise reduction is decreased, in which case, the present invention willnot be suitable for use in automobiles.

According to experiments, in a case that the walls 1 were attached ontwo sides of the present invention and the sectional area for expellingthe exhaust gas through the present invention was 4 cm×⁴ cm and thelength of the present invention was 60 cm, the quantity of the noisereduction was a little less than 20 dB. This is not suitable for theautomobile since such a degree of noise in the automobile is too high.

On the other hand, in order to mount the present invention on theautomobile, it cannot be made in a straight-line type due to the lowerstructure of the automobile.

Thus, a method for filtering the noise more effectively required for thepart of the present invention where the property of straighttransmission becomes strong as shown in FIG. 3 d.

If the muffler is provided with shorter walls 1 as shown in verticalsectional view of FIG. 1 a, the diameter of the present invention can bereduced by about 5 cm or as small as a typical exhaust pipe of anautomobile. Thus the present invention can be applied in accordance withthe lower structure of the automobile. Therefore, if forming curvatures20 at the part where the property of straight transmission becomesstrong as shown in FIGS. 1 b and 2 b, it will be an effective method forreducing the noise.

After the noise propagates about 30 cm into the pipe of the presentinvention, experiments show that the property of straight transmissionbecomes strong. FIG. 1 a shows a cross sectional view of the presentinvention having a curvature 20 in order to improve the effect of noisereduction. The noise enters from the left side and proceeds to the rightside. As disclosed in the above, while the noise in the usual exhaustpipe maintains the property of spherical wave, being reflected afterbeing bumped against the inner side of the exhaust pipe, the noiseentering into the present invention becomes strong in the property ofstraight transmission.

Therefore, as shown in FIG. 1 a, 1 f forming the curvatures 20 at theparts where the property of straight transmission becomes strong, mostof the noise can be effectively blocked by the walls 1 in the curvatures20. That is, the noise enters the space between the walls 1 in thecurvature 20 and is blocked by the walls, which is different from thecase of the exhaust gas (refer to FIG. 1 a).

Accordingly, most of the noise is blocked by the walls 1 in thecurvatures 20 and only the diffracted sound proceeds to the outlet 12.Although the property of straight transmission becomes strong, anothernoise having the property of spherical wave is generated at both ends ofthe proceeding surface, with the intensity of the sound energy dropping,which is the diffracted sound.

The diffracted sound becomes strong again in the property of sphericalwave since it is newly generated. That is, the noise passing through thecurvature 20 becomes strong in the property of spherical wave, thus theratio of noise reduction by the walls 1 can be significantly increased.

Although it is not yet determined what the mathematical expression forhow much the noise loses the sound energy in the moment when the noiseis blocked by the wall 1 in the curvature 20, the obvious fact is thatthe noise intensity at the outlet 12 is equal to the noise intensity inthe case of hearing the noise behind the soundproofing wall. Since thenoise proceeding to the outlet 12 is only a diffracted sound, most ofthe noise is reechoed to the inlet 11 by being blocked by the walls 1 ofthe curvature 20 and cannot proceed to the outlet 12. Thus, the noise inthe outlet 12 is heard as if the noise was heard behind a soundproofwall 1. Therefore, in order to improve the effect of noise reduction,straight portions 30 and curvatures 20 should be properly arranged whendesigning the muffler according to the present invention as shown inFIG. 1 b.

The noise filtered by the walls 1 experiences a decrease in soundpressure, which will be discussed hereinafter in order to find outwhether the filtered noise is found at the outlet 12. The filtered noiseenters the space between the walls 1 and is bumped against the body 13of the present invention and then is reflected toward the center of thepresent invention.

It is noticed from FIG. 3 d that the noise strength filtered by thewalls 1 is weaker than that of the noise proceeding that is not beingfiltered by the walls 1.

Also, referring to FIG. 3 a, the noise, which is filtered by the walls 1and reflected by the body of the present invention and then comes out tothe center of the present invention, experiences space expansion at thecenter of the present invention and is weakened, thus only some of thenoise proceeds to the outlet 12. Thus, the noise proceeding to theoutlet 12 among the noise filtered by the walls 1 has a much weakerintnesity as compared with the noise not filtered by the walls 1.

Therefore, the effect of noise reduction can be obtained sufficiently bylowering the intensity of the noise not filtered by the walls 1 to thedesired level. This also means that the noise intensity filtered by thewalls 1 becomes very low at the point of the outlet 12 so that thefiltered noise cannot influence the performance of the muffler accordingto the present invention.

As disclosed in the above, in order to reduce the noise effectively,Equation {circle over (1)} should be satisfied, and in order to improvethe ratio of noise reduction, the curvatures 20 should be designed inthe muffler.

If applying the present invention in accordance with the lower structureof automobiles or other applications, the effect of noise reduction canbe sufficiently obtained.

As shown in FIG. 1 a, if one curvature 20 is added to the muffler, thenoise is reduced by about 15 dB. Thus, if several curvatures are appliedto the muffler as shown in FIG. 1 b, the effect of noise reduction willbe significantly increased so that the muffler according to the presentinvention can be effectively used for the automobile.

As the length of the wall L is made several millimeters shorter as shownin the vertical sectional view of FIG. 1 a and subsequently the diameterof the present invention is only several millimeters larger than that ofa typical exhaust pipe, the noise can be reduced sufficiently by addingcurvatures 20 to the automobile as shown in FIG. 1 b.

Also, if the condensed water can be discharged, the life span of themuffler can be significantly extended. If the length of the wall islengthened and both ends of the present invention have open ends 11′ asshown at the left side of FIG. 6, the secondary noise can be generatedby the conflict between the last wall 1 and the exhaust gas beingexpelled to the atmosphere when the speed of the exhaust gas is high.For example, in case of 2000 cc CRDI diesel automobiles, if designingthe wall to the dimensions of 4 cm×4 cm×1 mm and the sectional area forexhaust the gas is 4 cm×4 cm, the exhaust gas begins to bump against thewalls 1 and to cause the secondary noise at RPM 2500, and the noisebecomes louder at RPM 3000.

Accordingly, in case that the present invention is used for theautomobile, the muffler should be designed in a manner that the size ofthe wall 1 is small and the secondary noise is not generated by theconflict the wall 1 and the exhausting gas. Thus, for this purpose, asshown in FIG. 6, the two ends 12 a of the muffler are arranged to benarrower. Conversely, the sectional area of the inlet end 11′ of themuffler is arranged to be wider so that the speed of the exhaust gas isreduced. In case of 2000 cc CRDI diesel automobiles, when the sectionalarea of one end 11′ of the present invention was (4 cm×4 cm)×2, therewas no secondary noise at RPM 3500.

The present invention can be applied to all the noise generatingmechanisms. Particularly, the present invention is useful for noisereduction in the noise generating mechanisms using an internalcombustion engine.

In addition, the present invention can be applied to apartments toreduce the noise between floors, for example, drainage pipes forbathroom. FIG. 4 d shows a model for blocking the bathroom noise. Whilethe noise proceeds in the direction of the arrows, it is blocked twotimes. The sound pressure of the noise is rapidly decreased by filteringtwo times and the filtered noise proceeds toward a ventilating openingbetween the floors. If attaching this type of noise reduction device toevery floor, the bathroom noise is blocked four times by the walls 1, sothat the noise becomes significantly weaker.

FIG. 4 e is a model for reducing the noise from a helicopter's engine.If attaching this type of noise reduction device (a thin plate issufficient for the device) to the engine, the noise can be reduced byover 10 dB without any influence on the output of power and aviation ofthe helicopter. If desired, the noise from propellers of a submarine canalso be reduced. Therefore, the present invention can be applied to allkinds of sound sources.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit and scope of the invention. Thepresent invention covers the modifications and variations thereofprovided they come within the scope of the appended claims and theirequivalents.

1. A noise reduction device having an inlet and an outlet and formed inthe shape of a pipe, comprising walls provided in a body thereof,thereby filtering some of the noise passing through the device andreducing noise at the outlet.
 2. The noise reduction device as claimedin claim 1, wherein the body is arranged using straight sections andangled sections.
 3. The noise reduction device as claimed in claim 1,wherein the quantity of walls and angles formed between the walls andbody may vary to change the overall performance of the noise reductiondevice.
 4. The noise reduction device as claimed in claim 1, wherein thewall is provided with protrusions and depressions.
 5. A noise reductiondevice, comprising: a pipe-shaped body having an inlet and an outlet;and a plurality of walls provided in the body and partially protrudingfrom the inner surface of the body towards the inner part of the body,to filter noise propagating from the inlet to the outlet, whereby thenoise intensity exiting the outlet is less than the noise intensityentering the inlet.
 6. The noise reduction device as claimed in claim 5,wherein the body is arranged using straight sections and angledsections.
 7. The noise reduction device as claimed in claim 5, whereinthe quantity of walls and angles formed between the walls and body maybe varied to change the overall performance of the noise reductiondevice.